North Korea recently threatened to launch an “unimaginable” strike on the United States while Central Intelligence Agency (CIA) director Mike Pompeo warned that Pyongyang is just months away from perfecting itsmissile reentry and nuclear warhead miniaturization technology.

But can current US missile defenses shoot down North Korean intercontinental ballistic missiles (ICBMs) aimed at the American mainland? What happens if Pyongyang uses decoy warheads or fires missiles in mass quantity at American targets?

And what ultimately makes more sense: building highly advanced antimissile systems or pursuing nonproliferation strategies to convince Pyongyang to curb its nuclear ambitions?

Greg Thielmann and Angelo Codevilla are respected US defense experts on opposed sides of the debate. Both worked at one time for the US Senate Select Committee on Intelligence. Codevilla helped conceive the “Star Wars” programs of former President Ronald Reagan administration’s Strategic Defense Initiative.

US former intelligence official and defense expert Greg Thielmann

Thielmann is a nonproliferation specialist on the board of the Washington-based Arms Control Association who served as a senior US State Department intelligence official toward the end of a 25-year career in the US Foreign Service.

Neither man believes Pyongyang’s rockets pose an immediate danger to the continental US, but both say a more serious threat looms.

Codevilla says a long-term solution lies in reactivating development of space-based radars and other anti-missile technologies mothballed at the end of the Cold War to facilitate various arms control pacts. He also asserts Washington must drop what he calls a de facto policy of not defending the US against Russian and Chinese missiles.

Antimissile defense expert Angelo Codevilla

Thielmann argues that deploying new antimissile systems while refusing to negotiate with North Korea will trigger an endless arms race that could lead to a catastrophic war. He also says it’s unrealistic to think the US can develop a workable strategic antimissile defense against Russia and China.

Are current US antimissile systems really capable of downing nuclear-tipped North Korean missiles fired at the US mainland?

Thielmann: Although North Korea has now flight-tested a long-range ballistic missile capable of reaching the US mainland, it is doubtful that it currently has a reliable nuclear warhead for that missile. The absence thus far of any North Korean efforts to receive downrange reentry telemetry for these tests is a revealing indicator that it cannot yet be confident it has a survivable nuclear warhead design for ICBMs. It is plausible, however, that it will have an operational, nuclear-tipped ICBM by the end of the decade.

Codevilla: Current US antimissile systems were designed, scrupulously, to do no less — and no more — than to defend against a few fairly crude missiles from North Korea. No more is needed to defend against what North Korea has today. Trouble is, North Korea is rapidly building missiles that overwhelm these defenses quantitatively and, to some extent, qualitatively as well.

How successful would present antimissile systems be — factoring in that Pyongyang might use decoy warheads or employ other countermeasures to thwart defenses?

Thielmann: The tactical and regional missile defenses currently deployed by the US, South Korea, and Japan — Patriot Advanced Capability-3 (PAC-3), Terminal High Altitude Area Defense (THAAD), and Standard Missile 3 (SM-3) — would be expected to attrit a significant portion of incoming short and medium-range North Korean missiles.

But in spite of the US$40 billion expended on the US strategic Ground-based Midcourse Defense (GMD) system, the type of GMD interceptors based in Alaska and California have only been successful in half of their highly-scripted tests to date. They would be even less successful against a real-world North Korean launch of multiple missiles with simple decoys, which are well within North Korea’s capability to develop and deploy.

Codevilla: Decoy warheads pose zero problem to any and all US antimissile systems. The US “wrote the book” on these things. Whatever faults these systems have, inability to deal withdecoys is not one of them.

North Korea’s other countermeasure — namely lofted trajectories to increase the warhead’s arrival speed – however is serious. But speed of arrival is a serious problem precisely and only because the US government has refused to build the information network that allows for early launch of interceptors.

Missile defense is essentially a time-distance problem. So long as US surface-based interceptors must rely for fire control on essentially co-located sources of information, the speed of incoming targets will degrade performance and load the components with heavy burdens.

If current antimissile systems are inadequate, can the US develop more advanced systems that can reliably intercept missiles fired by North Korea at the US or its allies?

Thielmann: The US is continually improving its ballistic missile defenses and it can develop more advanced systems. However, as with the US and Soviet Union during the Cold War, the cost exchange ratio is very much in favor of offense over defense — that is, it is much less expensive to build and deploy offensive missiles than to deploy ballistic missiles that can effectively intercept them.

Moreover, while relatively effective missile defenses — scoring, for example, an 80% success rate — could contribute significantly to defense against conventionally armed missiles, it could prove a catastrophic failure in attempting to defend a city against nuclear-tipped missiles.

Codevilla: Because the basic calculus of missile defense is the same time-distance problem, the solution has to be based on early detection, tracking and commitment of interceptors.

Are separate challenges involved in developing improved antimissile systems for the US mainland versus allies like South Korea and Japan that are much closer to North Korea? What are they?

Thielmann: Yes. Shorter-range missiles that can threaten US allies in Northeast Asia are more numerous and afford less warning time. So even relatively effective systems deployed by the US and its allies can be overwhelmed in continuing barrage attacks. But less numerous longer-range systems pose other challenges.

ICBM warheads reenter the atmosphere at much greater speeds than shorter-range systems. Moreover, since they are targeted while still in space where it is very difficult to distinguish warheads from decoys, they require much more sophistication in having a chance to defeat countermeasures.

Codevilla:South Korea’s and Japan’s location argues even more strongly for a solution based on early detection, tracking and commitment of interceptors — and leaves no doubt that that solution lies only in orbit-based, infrared systems. In the 1980s, the US was developing such a Space Based Infrared System (SBIRS)-low network of satellites. It was canceled when arms controllers pointed out, correctly, that such a network would have enabled relatively easy interception of Russian and Chinese missiles as well as of North Korean and Iranian ones.

Is negotiating with North Korea to curb its nuclear weapons and missile programs through a nonproliferation approach still viable and preferable to focusing on antimissile screens?

Thielmann: Deploying missile defenses while refusing to negotiate offers the prospect of an endless race to deploy ever more arms, with the prospect of ever more catastrophic destruction in the event of war. Negotiating a freeze on nuclear and missile tests as an interim step toward ultimate denuclearization is a better option.

North Korea already has a credible deterrent, because of US “worst case” analysis, but it must test further before having reliable nuclear operational forces. Focusing on missile defenses alone will only lead to a larger and more capable offensive threat – not only from North Korea, but also from China and Russia, which fear that their own deterrents will otherwise be jeopardized by US missile defense improvements.

Codevilla: Negotiating with North Korea has been an errand in which Western fools have shown just how foolish they are.

Most current US antimissile systems are land or sea based. Is it possible to develop more effective systems — such as space-based lasers or other alternative defenses to intercept North Korean missiles?

Thielmann: There is a reason that even the Star Wars enthusiasts of the Reagan and [George H.W.] Bush senior administrations did not deploy missile systems in space. Positioning such systems is much more expensive and requires more time than the steps necessary for opponents to effectively counter them.

Codevilla: A December 4, 1994 New York Times science section devoted a page, complete with drawings, to a story titled “Space-based laser nearly ready to fly.” In fact, such a missile-killing prototype was ready for trials. It was canceled because it would have been very useful against missiles fired from anywhere in the globe. A scaled-down, land-based version shot down Katyusha rockets over Israel. The elements of such a system don’t have to be invented. They exist.

Can more advanced alternative defenses be developed in time to deal with the current threat from North Korea?

Thielmann: Given the track record of the GMD system, it is unlikely the US would be able to successfully intercept all of even a small salvo of North Korean ICBMs fired at the US mainland by 2020. Given the inherent advantages of offenses over defenses, it is unlikely that US missile defense advances could keep pace with likely improvements in North Korean missile numbers and countermeasures.

Codevilla: The heart of the problem lies in US policy which — rhetoric notwithstanding, and which it’s consistently applied over a half century — is to put no obstacles in the path of Soviet/Russian and Chinese missiles fired at the United States. This is what the US ruling class understood as the “spirit” of the 1972 ABM treaty, the key provisions of which (as interpreted by Americans) have become unexamined axioms for the policy community, the military and industry.

The first axiom was that no orbital systems may “substitute for” radars, and that radars as well as interceptors must be together as sites. A “site” implies that the interceptors and radar/fire control systems are in proximity to each other. The Americans have further interpreted that to mean that although the radar and fire control systems at any given site can use information from anywhere, none of that “remote” info may be used to actually program and launch the interceptor for that site.

An exception was made for the interceptors at Vandenberg Air Force Base in California, which are controlled by systems in Alaska. But even this “fudging” has only resulted in a current “National Missile Defense” system consisting of a single radar/fire control system plus a maximum of 44 interceptors, based mostly in Alaska that purports, or rather pretends, to defend US territory.

This arrangement so increases the distance that the interceptors must travel and so shortens the time in which the interceptors must do it that the interceptors have to be huge. Current “employment doctrine” calls for devoting two interceptors to each incoming warhead because those who set the system’s requirements chose to require that the interceptors collide with the incoming warhead directly — without the aid of any (explosive) warhead.

The consequent burden on the guidance system is very great. In short, this system is un-expandable. Hence, so successful was this system in its primary objective of posing no problem whatever to Russian and Chinese missiles, that it has posed very little problems to ones from North Korea.

The second axiom was that the US was to have no antimissile weapons based on “other physical principles”— that is, no orbit-based lasers. These are the ultimate antimissile weapon which, until recently, only the US was capable of building.

If developing such alternative defenses is possible and worthwhile, what must the US do to develop them?

Thielmann: The only way alternative defenses would be possible and worthwhile would be for all space-faring nations to collaborate in efforts to counter ballistic missile threats from the four nuclear-capable states not party to the nuclear Non-Proliferation Treaty (NPT). Such cooperation between the US, Russia and China is not currently in the cards.

Codevilla: All it takes for the US to develop them is the decision to defend itself against missiles from anywhere.

Are we looking at a situation where no matter what the US does, it’s likely that some North Korean missiles will get through and strike the US mainland in a war?

Thielmann: Yes. For this reason, under current political circumstances, keeping the US nuclear deterrent credible rather than pursuing the chimera of making strategic missile defenses effective is the best assurance that such an attack will not occur.

Codevilla: No. First, North Korea has zero intention of starting a war that would be the end of its elites’ golden lives. The danger from North Korea’s nukes and missiles comes from the fact that Pyongyang is showing the US to be an impotent, defenseless paper tiger.